Capacitive sensors utilize a conductive element and a proximate ground plane or one or more proximate conductive elements separated by a dielectric material to form one or more capacitive touch elements. Each capacitive touch element exhibits a capacitance that can vary according to a proximity of a mass referred to herein as a “dielectric mass.” The dielectric mass may be any material proximate to the capacitive touch element which changes the overall dielectric strength of the capacitive touch element. For example, a human finger or other animal digit or body part, a fluid flow, an article of manufacture passing by on an assembly line, a tooth of a rotating gear and the like may all constitute dielectric masses. It is noted that the terms “capacitive sensor” and “capacitive touch sensor” are used interchangeably herein. For purposes of this disclosure, the latter term is not to be construed as requiring physical contact of a human digit with the sensor.
A capacitive sensor may consist of a single capacitive touch element or multiple capacitive touch elements. A single touch element sensor may be used in applications ranging from a simple on/off switch to counting applications and relative measurement of a distance of one or more proximate dielectric masses to the touch element. Touch elements of a multi-element capacitive sensor may be organized into a two-dimensional matrix and used to sense a position of a dielectric mass relative to the multi-element matrix.
Electronic circuitry used to detect, amplify, filter and otherwise process capacitive sensor signals is referred to herein as “capacitive touch detection apparatus.” Capacitive touch detection apparatus generates one or more output signals or values as relative or absolute measures of capacitance indicating the proximity of a dielectric mass to the sensor. Capacitive sensors and capacitive touch detection apparatus are traditionally susceptible to electromagnetic interference (“EMI”) due to their high impedance characteristics. Such EMI may include power line noise, energy-saving lamp noise, noise from switching power supplies, clock and data line noise, and so forth. Fundamental and harmonic frequencies associated with EMI may overlap frequencies of capacitive sensor signals. Such overlap may cause the capacitive touch detection apparatus to output erroneous values of capacitance and to consequently mis-interpret the proximity or position of a dielectric mass to the sensor.